Why Doesn’t Java

Have Instant

Turnaround?

Anton Arhipov

@antonarhipov

Product Lead at ZeroTurnaround

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Turnaround cycle

Make a change

Build, deploy,

wait

Check the

change

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What about others?

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Why Java is heavier than others?

Dev << Prod

Operations

Standards

Vendors

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A typical web application build

Package everything in a WAR/EAR

Package modules in JARs

Compile classes

Copy static resources

Resolve dependencies

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Exploded layout

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Automatic building

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Deployment by linking

• ln -s

• Symlinks can point to any file

Linux symbolic links

• Sysinternals junction utility on NTFS partitions, included in Windows 7

• Can only link to local directories and must be careful when deleting

Windows symbolic links

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Help!

is downloading the internets!

2008 => 2011

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2008 => 2011

this works:

mvn jetty:run

others?

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App Server

getResource(“hello.html”)

Workspace

read(“src/main/.../hello.html”)

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A typical web application build

Package everything in a WAR/EAR

Package modules in JARs

Compile classes

Copy static resources

Resolve dependencies

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Why code reloading is so hard?

Externalized Temporary

Serializable Derivative

State

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Reloading an Object

MyObject

MyObject.class

OldClassLoader NewClassLoader

MyObject.class

MyObject Recreate the object

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Web Deployment

Classes

Libraries

OldClassLoader NewClassLoader

Sevlet New

Classes

New

Libraries

Sevlet

Session Session

init()

App

State

App

State

Serialize/deserialize

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Twin ClassLoader Issues

JVM

Classes

Libraries

OldClassLoader NewClassLoader

Objects

and Code

Classes

Libraries

Objects

and Code

OutOfMemoryError

ClassCastException

…

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2008 => 2011

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Frameworks

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2008 => 2011

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Old Component

ClassLoader

New Component

ClassLoader

Class Object

Component State

New

Class

New

Object

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JVM Languages

Class-based

languages have same

limitations as Java

Groovy

Jython

Non-class based

languages can have

better support

JRuby

Clojure

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HotSwap

MyObject

MyObject.class

OldClassLoader

Code

101000101 100010010

Debugger

HotSwap

New Code

111000100 101010010

New Code

111000100 101010010

User saves class

from IDE

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JRebel Class Reloading HotSwap JRebel

Changing method bodies + +

Adding/removing methods - +

Adding/removing constructors - +

Adding/removing fields - +

Adding/removing classes - +

Adding/removing annotations - +

Replacing superclass - -

Adding/removing

implemented interfaces - -

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JRebel

MyObject

MyObject.class

OldClassLoader

Code

101000101 100010010 New Code

111000100 101010010

New Code

111000100 101010010

JRebel

agent

MyObject.class file

changed

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Classes

JRebel

MyObject

MyObject.class

OldClassLoader

Code

101000101 100010010 New Code

111000100 101010010

New Code

111000100 101010010

JRebel

agent

MyObject.class file

changed

Configuration

(XML, annotations, …)

Fra

me

wo

rk

Configuration changed

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IDEs Containers Frameworks

Build Tools

JRebel Integration

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Who is already using JRebel? Air / Auto Banking & FSI Web IT Telco

Healthcare

Consulting Fashion/Entertain

ment

Over 40 million builds, redeploys & restarts

prevented for 20,000+ Java developers

(how awesome is that?)

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<container-descriptor>

<fast-swap>true</fast-swap>

</container-descriptor>

weblogic-application.xml

Oracle Weblogic FastSwap

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Q: Why Doesn’t Java Have

Instant Turnaround?

A1: Other languages/platforms aren’t

much better!

A2: Reloading code is easy, preserving

state is hard!

A3: It’s better than it used to be!

A4: Play!, Tapestry 5 and Grails do that!

A5: But what about JRebel?

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Q?

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And also…

Instant, online rollout and rollback of

changes to production Java EE apps

for any deployment size.